Fentanyl is a μ-opioid receptor agonist with analgesic potency approximately 80-100 times that of morphine. In clinical settings, fentanyl exerts its principal pharmacologic effects on the central nervous system. Its primary actions are analgesic and sedation.
The analgesic effects of fentanyl are related to the blood level of the drug. In general, the minimum effective concentration and the concentration at which toxicity occurs rise with increasing tolerance to any and all opioids. The rate of development of tolerance may vary widely among individuals. All opioid mu-receptor agonists, including fentanyl, produce dose dependent respiratory depression. The risk of respiratory depression is typically less in patients receiving chronic opioid therapy who develop tolerance to respiratory depression and other opioid effects. Serious or fatal respiratory depression can occur, even at recommended doses, in vulnerable individuals.
Orally administered fentanyl is subject to first pass effect metabolism as upwards of 50% or more of orally administered fentanyl is not absorbed. Other forms of delivery such a parenteral, buccal, and transdermal have been utilized to decrease or avoid this first pass effect for fentanyl.
Fentanyl is currently available in injectable form, as a lozenge (e.g. Actiq®), and as a transdermal system (e.g., Duragesic® 25, 50, 75, and 100 μg of fentanyl per hour). Duragesic® provides continuous systemic delivery of fentanyl for approximately 72 hours. Duragesic® is indicated in the management of chronic pain in patients requiring continuous opioid analgesia for pain that is not optimally managed with lesser means such as acetaminophen-opioid combinations, non-steroidal analgesics, or prn (as needed) dosing with short-acting opioids. Duragesic® is typically not suitable for patients experiencing acute pain due to the delay in absorption of the fentanyl through the patch, or postoperative pain because serious or life-threatening hypoventilation could result.
Actiq® is a solid formulation of fentanyl citrate, intended for oral transmucosal administration. Actiq® is a lozenge attached to a handle similar in shape to a lollipop. The handle is purportedly to allow the Actiq® unit to be removed from the mouth if signs of excessive opioid effects appear during administration. Actiq® is indicated for the management for breakthrough cancer pain in patients with malignancies who are already receiving and who are tolerant to opioid therapy for their underlying persistent cancer pain. Actiq® is contraindicated in the management of acute or postoperative pain.
Sublingual tablets and lozenges (e.g., Actiq®) which may be used for acute pain or breakthrough pain have certain disadvantages. A disadvantage, amongst others, is that after intake the active agent in these pharmaceutical agents must first be released and dispersed prior to being available for resorption in dissolved form. In addition, the absorption pharmacokinetics of fentanyl from Actiq® may vary depending on the fraction of the dose that is absorbed through the oral mucosa and the fraction swallowed. Further, certain lozenges may be in the form of a candy which require medical supervision and may be socially questionable.
There exists a need in art for a sublingual formulation including fentanyl, a pharmaceutically acceptable salt thereof, or derivative thereof, which is suitable for effective pain management.